Refactoring transparence tab code

Move transparence tab code out from Area tab code.

Change-Id: Ia7276aa3b1c438b6c8cff89ab5ca3752ff6bcc0e
Reviewed-on: https://gerrit.libreoffice.org/24368Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>

cui/Library_cui.mk

@@ -205,6 +205,7 @@ $(eval $(call gb_Library_add_exception_objects,cui,\
     cui/source/tabpages/tplnedef \
     cui/source/tabpages/tplneend \
     cui/source/tabpages/tpshadow \
+    cui/source/tabpages/tptrans \
     cui/source/tabpages/transfrm \
     cui/source/uno/services \
 ))